The objective of this research is to elucidate the biosynthetic origin, from primary metabolites, of the oxathiazepine-bearing (OTAP) eudistomins in the ascidian Eudistoma olivacium. These potently antiviral (HSV, Vaccina) metabolites seemingly derive from tryptamine, cysteinal and S-adenosylmethionine, although alternative precursors are considered. Potential intermediates along the biosynthetic path are identified and radiolabelled syntheses of these intermediates are proposed. Using cell-frree methodology previously developed to study biosynthesis in other colonial marine invertebrates, these putative precursors will be tested for incorporation into the OTAP eudistomins. Double-label and degradative schemes will be employed to determine the specificity of the precursors and thus rule out catabolic processes that might lead to incorporation of radioactivity. The results of this biosynthetic study of the OTAP eudistomins could lead to subsequent studies aimed at identification of genetic material in E. olivacium that codes for these metabolites. Exploitation via genetic engineering could then make available commercial quantities of these potential drugs, obviating the problem of limited natural-source availability.